Display screen or portion thereof with transitional graphical user interface



FIG. 1 is the first image in a sequence of a display screen or portion thereof with transitional graphical user interface showing our new design;

FIG. 2 is the second image thereof; and,

FIG. 3 is the third image thereof.

The outermost dashed broken line rectangle illustrates a display screen. The remaining dashed broken lines illustrate portions of the graphical user interface. None of the broken lines form part of the claimed design.

The appearance of the graphical user interface sequentially transitions between the images shown in FIGS. 1-3 . This process or period in which one image transitions to another image forms no part of the claimed design. 

CLAIM The ornamental design for a display screen or portion thereof with transitional graphical user interface, as shown and described. 